JP2010256740A - Developing device and image forming apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device preventing a decrease in image density during continuous printing, and also to provide an image forming apparatus including the developing device. <P>SOLUTION: In an inter-job toner concentration correction, a control part 39 sets VmagP(DC) to a set value V2 to form a first patch image, and in an inter-sheet toner concentration correction, the control part 39 sets VmagP(DC) to a value, which is obtained by adding correction bias ΔV to the set value V2, to form a second patch image, and then the control part 39 calculates CTD from the result of image density detection of the first and second patch images by an image density detection sensor 43 to execute the toner concentration correction by adjusting a toner supply amount on the basis of the calculated CTD. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a developing device mounted on an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and an image forming apparatus including the developing device, and more particularly, to a developing roller using a two-component developer having a magnetic carrier and toner. The present invention relates to toner density control of a developing device that holds only a charged toner and develops an electrostatic latent image on an image carrier.

  Conventionally, as a development method using dry toner in an image forming apparatus using an electrophotographic process, a one-component development method using no carrier and a two-component developer charging a nonmagnetic toner using a magnetic carrier are used. In addition, a two-component development system is known in which an electrostatic latent image on an image carrier (photoconductor) is developed by a magnetic brush composed of toner and a carrier formed on a developing roller.

  The one-component development method is suitable for high image quality because the electrostatic latent image on the image carrier is not disturbed by the magnetic brush. On the other hand, the toner is charged by the charge roller, and the elastic regulating blade is used on the development roller. In order to regulate the layer thickness, the toner additive adheres to the charge roller, the charging ability is lowered, and it is difficult to stably maintain the charge amount of the toner. In addition, toner may adhere to the regulating blade, resulting in non-uniform layer formation and image defects.

  In the case of color printing in which color superposition is performed, since the color toner is required to be transparent, it needs to be a non-magnetic toner. Therefore, in a full-color image forming apparatus, a two-component development system in which toner is charged and conveyed using a carrier is often employed. However, the two-component development method can maintain a stable charge amount for a long time and is suitable for extending the life of the toner, but is disadvantageous in terms of image quality due to the influence of the magnetic brush described above.

  As one of means for solving these problems, when a developer is transferred onto a developing roller (toner carrier) installed in a non-contact manner with respect to the image carrier using a magnetic roller (toner supply member), A developing method is proposed in which only a non-magnetic toner is transferred onto the developing roller while leaving the magnetic carrier on the magnetic roller to form a thin toner layer, and the toner is attached to the electrostatic latent image on the image carrier by an AC electric field. Has been.

  The toner density control in the developer may be performed by adjusting the toner replenishment amount based on the toner density in the developer detected by a magnetic permeability sensor or the like, while the patch image (reference toner image) is displayed. In some cases, the toner replenishment amount is adjusted based on the image density detection result of the patch image. However, since the image density of the patch image decreases with time during continuous printing, if the toner replenishment amount is increased in accordance with the decrease in the image density, the toner replenishment amount becomes excessive and image defects such as fogging may occur. is there.

  Therefore, for example, Patent Document 1 discloses a toner density detection unit that detects the density of toner in a developer and an image density that optically detects the density of a test pattern (patch image) formed on an image carrier. Detecting means, and when the toner density detected by the toner density detecting means reaches an upper limit of a preset toner density, the toner supply based on the detection output of the image density detecting means is stopped, thereby A method is disclosed in which a change in image density is also prevented by changes and fluctuations over time of the charging potential, exposure, developer, etc. in the body drum.

Japanese Patent Laid-Open No. 2-50183

  However, in the method of Patent Document 1, the toner density control is performed by switching from the control based on the image density detection result to the control based on the toner density detection result according to the size of the patch image. This is not a method for preventing a decrease in image density of the reference toner image.

  Here, during continuous printing, toner gradually adheres to the surface of the developing roller, and charges tend to accumulate on the surface of the roller. When electric charges are gradually accumulated on the developing roller surface over time until saturation is reached during continuous printing, the potential of the roller surface rises, and the DC potential difference (effective potential) between the developing roller and the magnetic roller is increased. Get smaller.

  As a result, in the above-described two-component development method, the amount of toner supplied from the magnetic roller to the development roller during continuous printing may decrease with time, and the image density may decrease. As a result, the amount of toner provided to the patch image is reduced, affecting the image density detection result of the patch image, and further affecting toner density correction.

  In addition, when toner density correction is performed based on a patch image during a printing operation and during a predetermined printing during continuous printing, the image density of the patch image decreases with time during continuous printing as described above. Compared to the correction of the toner density during the printing operation, the density of the patch image is lowered during the correction of the toner density during the continuous printing, and an error occurs in the correction of the toner density.

  In view of the above problems, an object of the present invention is to provide a developing device capable of preventing a decrease in image density during continuous printing and an image forming apparatus including the developing device.

  To achieve the above object, the present invention uses a developer containing at least a carrier and a toner, a toner carrier for supplying the toner to the image carrier, and a toner using a magnetic brush on the toner carrier. A toner supply member for forming a layer; voltage applying means capable of applying a DC bias and an AC bias to the toner carrier and the toner supply member; and an image density for detecting a density of a toner image formed on the image carrier. A developing device comprising: a detection unit; and a control unit that performs correction of toner density in the developer based on an image density detection result of a reference toner image formed on the image carrier by the image density detection unit. The control means can execute a first toner density correction between printing operations and a second toner density correction between predetermined printings during continuous printing. In the degree correction, a predetermined reference toner image forming DC bias is applied to the toner supply member, and in the second toner density correction, each time the predetermined integrated printing time is reached during the continuous printing, the reference toner is corrected. The reference toner image is formed by applying a predetermined correction bias to the toner supply member in addition to the image forming DC bias.

  In the developing device configured as described above, the control unit may vary the correction bias based on a continuous printing time until immediately before the second toner density correction is performed.

  According to the present invention, in the developing device having the above-described configuration, an environmental condition detection unit that detects an environmental condition is provided, and the control unit varies the correction bias based on an environmental condition detection result of the environmental condition detection unit. It is characterized by.

  According to the present invention, in the developing device configured as described above, the reference toner image forming DC bias for forming a color image is at least twice the reference toner image forming DC bias for forming a black image. Yes.

  According to the present invention, in the developing device configured as described above, the control unit varies the correction bias according to the reference toner image forming DC voltage.

  Further, according to the present invention, in the developing device having the above-described configuration, a toner density detection unit that detects a toner density in the developer is provided, and the control unit performs a third process based on a toner density detection result of the toner density detection unit. Toner density correction can be executed, and during the continuous printing, based on the toner density detection result of the toner density detection means and the image density detection result of the image density detection means, at least the second and third One of the toner density corrections is performed.

  The present invention also provides an image forming apparatus including the developing device having the above-described configuration.

  According to the first configuration of the present invention, in the first toner density correction between the printing operations, the control unit applies a predetermined reference toner image forming DC bias to the toner supply member to perform continuous printing. In the second toner density correction between predetermined printings, a predetermined correction bias is applied to the toner supply member in addition to the reference toner image forming DC bias every time a predetermined integrated printing time is reached, thereby forming a reference toner image. can do.

  As a result, even if the effective potential between the toner carrier and the toner supply member decreases with time during continuous printing, the effective toner potential can be prevented from decreasing at the time of the second toner density correction to form a reference toner image. Can do. Therefore, at the time of the second toner density correction, it is possible to prevent a reduction in the amount of toner carried on the toner carrying member and to prevent a reduction in the image density of the reference toner image. Accordingly, the image density of the reference toner image at the time of the second toner density correction can be brought close to that at the time of the first toner density correction, and the second toner density correction can be appropriately performed. Can be prevented.

  According to the second configuration of the present invention, in the developing device of the first configuration, the control unit varies the correction bias based on the continuous printing time until immediately before performing the second toner density correction. Thus, since the effective potential can be adjusted according to the state of adhesion of the toner to the toner carrying member, it is possible to more appropriately prevent the image density of the reference toner image from being lowered.

  According to the third configuration of the present invention, in the developing device having the first or second configuration, the environmental condition detection unit that detects the environmental condition is provided, and the control unit detects the environmental condition of the environmental condition detection unit. By varying the correction bias based on the result, the effective potential can be adjusted in accordance with the state of adhesion of the toner to the toner carrier, so that it is possible to more appropriately prevent the image density of the reference toner image from being lowered.

  According to the fourth configuration of the present invention, in the developing device having any one of the first to third configurations, the reference toner image forming DC bias for color image formation is used as the reference toner for black image formation. Since the effective potential can be adjusted according to the formation state of the reference toner image due to the characteristics of the toner or the like by setting it to at least twice the DC bias for image formation, the image density of the reference toner image can be prevented more appropriately. be able to.

  According to the fifth aspect of the present invention, in the developing device having any one of the first to fourth aspects, the control unit varies the correction bias according to the reference toner image forming DC voltage. Since the effective potential can be adjusted according to the effect of the toner attached to the toner carrier on the effective potential, it is possible to more appropriately prevent the image density of the reference toner image from being lowered.

  According to the sixth configuration of the present invention, in the developing device having any one of the first to fifth configurations, the toner concentration detection unit that detects the toner concentration in the developer is provided, and the control unit is configured to The third toner density correction can be executed based on the toner density detection result of the density detection means, and based on the toner density detection result of the toner density detection means and the image density detection result of the image density detection means during continuous printing. By executing at least one of the second and third toner density corrections, the toner density correction can be performed in more detail, and a decrease in image density can be prevented more appropriately.

  Further, according to the seventh configuration of the present invention, the image forming apparatus including the developing device having any one of the first to sixth configurations prevents the image density from being lowered even during continuous printing. Image formation can be performed.

1 is a schematic cross-sectional view illustrating an overall configuration of an image forming apparatus including a developing device according to an embodiment of the present invention. Side surface sectional view showing the configuration of the developing device of the present embodiment The figure which shows an example of the bias waveform applied to a developing roller and a magnetic roller The block diagram which shows the control path | route of the image development apparatus of this embodiment. Schematic diagram showing timing for performing T / C and CTD toner density correction The figure which shows an example of CTD based on the 1st patch image at the time of toner density correction between jobs in a black development device, and CTD based on the 2nd patch image at the time of paper toner density correction which does not add correction bias The figure which shows an example of TD of the 2nd patch image at the time of the paper toner density correction | amendment in the developing device for black. The figure which shows an example of CTD based on the 1st patch image at the time of toner density correction between jobs in a black developing device, and CTD based on the 2nd patch image at the time of paper density correction between papers which added correction bias. 7 is a flowchart showing a control procedure of a first control example of the developing device of the present embodiment. The figure which shows an example of TD of the 2nd patch image at the time of the toner density correction between paper in the low temperature low humidity environment in the developing device for black. 8 is a flowchart showing a control procedure of a second control example of the developing device of the present embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus including a developing device according to an embodiment of the present invention. Here, a tandem color image forming apparatus is shown. In the main body of the color image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  Photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors are disposed in the image forming portions Pa to Pd, and are formed on the photosensitive drums 1a to 1d. The transferred toner image is rotated clockwise in FIG. 1 by a driving means (not shown) and sequentially transferred onto the intermediate transfer belt 8 moving adjacent to each image forming unit, and then the secondary transfer roller 9. In this case, the toner image is transferred onto the transfer paper P at once, and further fixed on the transfer paper P in the fixing unit 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the secondary transfer roller 9 via a paper feed roller 12a and a registration roller pair 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used. A blade-shaped belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure unit 4 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning units 5a, 5b, 5c and 5d are provided.

  When the image formation start is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated by the exposure unit 4 to each of the photosensitive drums 1a to 1d. An electrostatic latent image corresponding to the image signal is formed on the top. Each of the developing devices 3a to 3d is filled with a predetermined amount of cyan, magenta, yellow, and black toner by a toner replenishing device 51 (see FIG. 2). The toner is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically attached, whereby a toner image corresponding to the electrostatic latent image formed by exposure from the exposure unit 4 is formed. It is formed.

  Then, after an electric field is applied to the intermediate transfer belt 8 with a predetermined transfer voltage, cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d by the intermediate transfer rollers (primary transfer rollers) 6a to 6d. Is transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched between an upstream conveyance roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the transfer paper P is conveyed from the registration roller 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and a full color image is transferred. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer paper P conveyed to the fixing unit 7 is heated and pressurized by the fixing roller pair 13 so that the toner image is fixed on the surface of the transfer paper P, and a predetermined full color image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed only on one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when images are formed on both sides of the transfer paper P, the transfer paper P that has passed through the fixing unit 7 is distributed to the paper transport path 18 by the branching unit 14, and the secondary transfer roller 9 with the image surface reversed. Re-conveyed. Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the transfer paper P on which the image is not formed by the secondary transfer roller 9 and conveyed to the fixing unit 7 to fix the toner image. , And discharged to the discharge tray 17.

  FIG. 2 is a side sectional view showing the configuration of the developing device of the present embodiment. Here, the developing device 3a disposed in the image forming unit Pa of FIG. 1 will be described, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus described. Is omitted.

  As shown in FIG. 2, the developing device 3a includes a developing container 20 in which a two-component developer (developer, hereinafter simply referred to as a developer) is accommodated, and the developing container 20 is first separated by a partition wall 20a. The first and second agitating chambers 20b and 20c are divided into toner (positively charged toner) supplied from the toner replenishing device 51 and mixed with a carrier to stir and charge the first and second agitating chambers 20b and 20c. The first stirring screw 21a and the second stirring screw 21b are rotatably arranged.

  Then, the developer is conveyed in the axial direction while being stirred by the first stirring screw 21a and the second stirring screw 21b, and the first and second are passed through developer passages (not shown) formed in the partition wall 20a. It circulates between the stirring chambers 20b and 20c. In the illustrated example, the developing container 20 extends obliquely upward to the left, a magnetic roller 22 is disposed in the developing container 20 above the second stirring screw 21b, and the developing roller 20 is disposed obliquely upward to the left of the magnetic roller 22. Rollers 23 are arranged opposite to each other. The developing roller 23 faces the photosensitive drum 1a on the opening side (left side in FIG. 2) of the developing container 20, and the magnetic roller 22 and the developing roller 23 rotate clockwise in the drawing.

  In addition, a magnetic permeability sensor 41 that detects the toner concentration in the developer is disposed in the developing container 20 so as to face the first stirring screw 21a. The magnetic permeability sensor 41 detects a toner ratio (toner concentration, T / C) with respect to a carrier in the developer and transmits an output signal to a control unit 39 (see FIG. 4) described later, thereby obtaining a T / C (toner). Density detection result) can be detected.

  The magnetic roller 22 includes a nonmagnetic rotating sleeve 22a and a fixed magnet roller body 22b having a plurality of magnetic poles (here, five poles) contained in the rotating sleeve. The developing roller 23 is composed of a non-magnetic developing sleeve, and the magnetic roller 22 and the developing roller 23 are opposed to each other at a facing position (opposing position) with a predetermined gap.

  Further, a spike cutting blade 25 is attached to the developing container 20 along the longitudinal direction of the magnetic roller 22 (front and back direction in FIG. 2), and the spike cutting blade 25 rotates in the rotational direction of the magnetic roller 22 (clockwise in the figure). Around the opposite position between the developing roller 23 and the magnetic roller 22. A slight gap (gap) is formed between the front end of the spike cutting blade 25 and the surface of the magnetic roller 22.

  The developing roller 23 is connected to a first bias circuit 30 that applies a DC voltage (hereinafter referred to as Vslv (DC)) and an AC voltage (hereinafter referred to as Vslv (AC)). A second bias circuit 31 for applying a voltage (hereinafter referred to as Vmag (DC)) and an alternating voltage (hereinafter referred to as Vmag (AC)) is connected.

  A voltage variable device 33 is connected to the first bias circuit 30 and the second bias circuit 31, and Vslv (DC) applied to the developing roller 23 based on a control signal from the control unit 39 (see FIG. 4). ), Vslv (AC) and Vmag (DC) and Vmag (AC) applied to the magnetic roller 22 can be varied.

  As described above, the first stirring screw 21a and the second stirring screw 21b circulate in the developing container 20 while the developer is being stirred to charge the toner, and the second stirring screw 21b causes the developer to move to the magnetic roller 22. Be transported. Then, a magnetic brush (not shown) is formed on the magnetic roller 22.

  After the layer thickness of the magnetic brush on the magnetic roller 22 is regulated by the ear cutting blade 25, the magnetic brush 22 is conveyed to the opposite portion between the magnetic roller 22 and the developing roller 23, and Vmag (DC) applied to the magnetic roller 22 and the developing roller 23. A toner thin layer is formed on the developing roller 23 by a potential difference (effective potential) with respect to Vslv (DC) applied to and a magnetic field with the fixed magnet roller body 22b.

  The thickness of the toner layer on the developing roller 23 varies depending on the resistance of the developer and the rotational speed difference between the magnetic roller 22 and the developing roller 23, but between the magnetic roller 22 and the developing roller 23 (hereinafter referred to as between the MSs). Can be controlled by the effective potential (hereinafter referred to as DS between MSs). When the DS between MSs is increased, the toner layer on the developing roller 23 becomes thicker, and when the DS between MSs is decreased, the toner layer becomes thinner. The range of DS between MSs during development is generally about 100V to 350V.

  FIG. 3 is a diagram illustrating an example of a bias waveform applied to the developing roller 23 and the magnetic roller 22. As shown in FIG. 3A, the developing roller 23 has a combined waveform Vslv (solid line) in which a rectangular wave Vslv (AC) having a peak-to-peak value of Vpp1 superimposed on Vslv (DC) is a first bias circuit. 30 applied. The magnetic roller 22 has a second composite waveform Vmag (broken line) in which Vmag (DC) has a peak-to-peak value of Vpp2 and a Vmag (AC) of a rectangular wave having a phase different from that of Vslv (AC). Applied from the bias circuit 31.

  Therefore, the voltage applied between the MSs is a composite waveform Vmag−Vslv having Vpp (max) and Vpp (min) as shown in FIG. Note that Vmag (AC) is set so that the duty ratio is larger than Vslv (AC). Actually, an AC voltage having a partially distorted shape is applied instead of a complete rectangular wave as shown in FIG.

  The toner thin layer formed on the developing roller 23 by the magnetic brush is conveyed to a facing portion between the photosensitive drum 1 a and the developing roller 23 by the rotation of the developing roller 23. Since Vslv (DC) and Vslv (AC) are applied to the developing roller 23, the toner flies due to a potential difference with the photosensitive drum 1a, and the electrostatic latent image on the photosensitive drum 1a is developed. .

  The remaining toner that is not used for development is conveyed again to the opposite portion between the developing roller 23 and the magnetic roller 22 and collected by the magnetic brush on the magnetic roller 22. Then, the magnetic brush is peeled off from the magnetic roller 22 at the same polarity portion of the fixed magnet roller body 22b, and then formed again on the magnetic roller 22 as a two-component developer uniformly charged with an appropriate toner concentration. And conveyed to the ear cutting blade 25.

  Further, an image density detection sensor (image density detection means) 43 is disposed at the downstream end of each of the developing devices 3a to 3d in the rotational direction of each of the photosensitive drums 1a to 1d so as to face the photosensitive drums 1a to 1d. (See FIG. 2). As the image density detection sensor 43, generally, an optical sensor including a light emitting element made of an LED or the like and a light receiving element made of a photodiode or the like is used.

  When measuring the toner adhesion amounts on the photosensitive drums 1a to 1d, if the measurement light is irradiated from the light emitting elements to the patch images (reference toner images) formed on the photosensitive drums 1a to 1d, the measurement light is converted into toner. Is incident on the light receiving element as light reflected by the drum surface and light reflected by the drum surface. As the patch image, a general substantially rectangular patch image can be formed.

  When the toner adhesion amount is large, the reflected light from the drum surface is shielded by the toner, so that the light reception amount of the light receiving element decreases. On the other hand, when the toner adhesion amount is small, the amount of reflected light from the drum surface increases, resulting in an increase in the amount of light received by the light receiving element. Therefore, the image density TD (image density detection result) of each color patch image can be detected by transmitting the output value of the received light signal based on the received reflected light amount to the control unit 39 (see FIG. 4).

  The image density detection sensor 43 can also be arranged outside the developing devices 3a to 3d in the image forming apparatus 100. For example, the image density detecting sensor 43 is upstream of the developing devices 3a to 3d with respect to the rotation direction of the photosensitive drums 1a to 1d. It can also be arranged downstream of the transfer rollers 6a to 6d.

  The image density detection sensor 43 can also detect a patch image transferred to the intermediate transfer belt 8, and in addition, the image forming apparatus 100 can transfer the patch images formed on the photosensitive drums 1a to 1d using a conveyance belt. In the case of an image forming apparatus of a direct transfer type that directly transfers to the transferred transfer paper P, a patch image transferred onto the paper P or a patch image transferred onto the transfer belt can be detected.

  Further, a temperature / humidity detection sensor 45 is provided in the image forming apparatus 100 as shown in FIG. The temperature / humidity detection sensor 45 can detect the environmental temperature / humidity (environmental condition) around the developing devices 3 a to 3 d and transmit an output signal to the control unit 39. The temperature / humidity sensor 45 can also be disposed on the outer surface or inside of the developing devices 3a to 3d.

  FIG. 4 is a block diagram showing a control path of the developing device of the present embodiment. Portions common to FIGS. 1 to 3 are denoted by the same reference numerals and description thereof is omitted. The developing devices 3a to 3d include a first stirring screw 21a, a second stirring screw 21b, a magnetic roller 22, a developing roller 23, a first bias circuit 30, a second bias circuit 31, a voltage variable device 33, a magnetic permeability sensor 41, an image. The configuration includes a concentration detection sensor 43, a temperature / humidity sensor 45, and the like.

  The storage unit 37 is composed of, for example, a readable / writable RAM (Random Access Memory). In addition to a control program related to the agitation and conveyance of the developer used by the control unit 39, the magnetic permeability used for T / C toner density correction described later. A T / C toner density correction parameter that associates T / C of the sensor 41 with Vcon is stored.

  In addition, the storage unit 37 stores a CTD toner density correction parameter that associates an output value of the image density detection sensor 43 with TD, CTD, and Vcon, which is used for CTD toner density correction described later. In addition, the storage unit 37 has environmental condition parameters for determining whether a predetermined accumulated printing time T1, a continuous printing time t1, which will be described later, and a temperature / humidity detection result of the temperature / humidity sensor 45 are predetermined environmental conditions. Remembered.

  Also, the storage unit 37 includes a set value V1 of VslvP (DC), a set value V2 of VmagP (DC) for forming the first patch image during the correction of the toner density between jobs in the CTD toner density correction, and the sheet interval. A correction bias ΔV such as a first correction bias ΔV1 and a second correction bias ΔV2 to be added to the set value V2 of VmagP (DC) for forming a second patch image at the time of toner density correction is also stored.

  The control unit 39 receives the output signal from the magnetic permeability sensor 41, calculates T / C based on the T / C toner concentration correction parameter stored in the storage unit 37, and adjusts Vcon (T / C toner concentration Correction and third toner density correction).

  Further, when the calibration mode is set by a key operation on an operation panel (not shown) or the like, the control unit 39 forms a first patch image, receives an output signal from the image density detection sensor 43, and stores the storage unit. 37 has a function of calculating TD and CTD based on the CTD toner density correction parameter stored in 37 and adjusting Vcon (inter-job toner density correction). Such a calibration mode can be set when the apparatus is turned on or between a predetermined number of continuous image forming processes (jobs).

  The control unit 39 has a function of counting the accumulated printing time T and a function of determining whether or not the predetermined accumulated printing time T1 has been reached during continuous printing. Each time the accumulated print time T reaches the predetermined accumulated print time T1 during printing, a second patch image is formed, an output signal from the image density detection sensor 43 is received, and the CTD toner density correction stored in the storage unit 37 is received. It has a function of calculating TD and CTD based on the use parameters and adjusting Vcon (inter-paper toner density correction).

Further, the control unit 39 has a function of changing the VmagP (DC) from V2 to V2 + ΔV1 or V2 + ΔV2 to form the second patch image when correcting the toner density between sheets. The accumulated printing time T represents the total printing time performed on each sheet P when one or more jobs are performed, and is reset when the inter-sheet toner density correction is performed.

The control unit 39 also has a function of measuring the continuous printing time t immediately before the inter-paper toner density correction is performed, a function of determining whether or not the continuous printing time t is equal to or longer than the predetermined continuous time t1, and the immediately preceding continuous printing time t. Has a function of setting VmagP (DC) from V1 to V1 + ΔV2 when is equal to or greater than t1. The continuous printing time t is the time from the start of printing in the job to the end of printing immediately before the correction of the toner density between papers when the predetermined cumulative time T1 is reached during one continuous printing (job). Represents.

In addition, the control unit 39 receives an output signal from the temperature / humidity detection sensor 45 and determines whether the temperature / humidity detection result corresponds to a low temperature / low humidity condition (for example, 10 ° C. and 15% RH or less). When the humidity detection result corresponds to a low temperature and low humidity condition, VmagP (DC) is changed from V2 to V2 + ΔV.
2 is set. Note that the storage unit 37 and the control unit 39 may be combined with the control unit and the storage unit of the entire image forming apparatus 100, or may be arranged independently to control the developing devices 3a to 3d.

  Next, T / C toner density correction using the magnetic permeability sensor 41 and CTD toner density correction using the image density sensor 43 will be described.

  As described above, the control unit 39 varies the control voltage Vcon for adjusting the toner supply amount of the toner supply device 51 in accordance with T / C calculated from the output signal of the magnetic permeability sensor 41, thereby changing the toner supply amount. The toner is supplied from the toner supply device into the developing container 20 through the toner supply port 20d. Thus, by changing the toner replenishment amount (that is, Vcon) to the developing devices 3a to 3d based on the magnetic permeability sensor 41, the toner density correction by T / C (T / C toner density correction, third color) is performed for each color. Toner density correction) is performed.

  Further, as described above, the control unit 39 adjusts the toner replenishment amount by changing Vcon according to TD and CTD calculated from the output signal of the image density detection sensor 43, and the toner replenishing port 20d is changed from the toner replenishing device. Thus, the toner is supplied into the developing container 20. As described above, by changing the toner replenishment amount (that is, Vcon) to the developing devices 3a to 3d based on the image density detection sensor 43, toner density correction by CTD (CTD toner density correction, first and second) is performed for each color. Toner density correction).

  FIG. 5 is a schematic diagram showing timing for performing T / C and CTD toner density correction. Although FIG. 5 shows only the upper limit side with respect to the target value of T / C, the same correction is performed on the lower limit side. In addition, the numerical values such as the target values shown in FIG.

  As shown in FIG. 5, the target value of T / C detected by the magnetic permeability sensor 41 is set to 482. The upper limit value of T / C is set to 502, and the threshold value is set to 522. In a range where T / C does not exceed the upper limit value 502 (T / C ≦ 502), Vcon is varied and adjusted so that T / C becomes the target value 482 by T / C toner density correction.

  On the other hand, when T / C exceeds the upper limit value 502 (502 <T / C), in the range where T / C does not exceed the threshold value 522 (502 <T / C ≦ 522), in addition to T / C toner density correction Thus, Vcon is varied and adjusted by CTD toner density correction. That is, Vcon is varied based on the T / C by the magnetic permeability sensor 41 so that T / C becomes smaller than the upper limit value, and the upper limit value and lower limit of the CTD are calculated based on the CTD calculated by the image density detection sensor 43. Vcon is corrected so as to be within the value. The CTD will be described later.

  As a result, if the T / C is less than or equal to the upper limit value 502, only the T / C toner density correction is performed again. On the other hand, when T / C exceeds 522 (522 <T / C), only CTD toner density correction is performed. As a result, when T / C is 522 or less, T / C and CTD toner density correction is performed as described above, and when T / C is 502 or less, only T / C toner density correction is performed as described above. .

  In the T / C and CTD toner density correction, the amount of one-time fluctuation of Vcon is within ± 5 bits by combining both toner density corrections, and the amount of one-time fluctuation of Vcon due to CTD toner density correction is ± 6. It can be set to be within bits. Here, 16 bits corresponds to a variation of 1% of T / C. However, the variation amount of Vcon is not particularly limited to such a value, and can be appropriately set according to the device configuration and the like.

  Next, details of CTD toner density correction using the image density detection sensor 43 will be described. Between jobs, a first patch image is formed with VslvP (DC) and VmagP (DC) set values as V1 and V2, and based on the detection result of the first patch image by the image density detection sensor 43 as described above. TD and CTD are calculated and Vcon is adjusted (inter-job toner density correction, first toner density correction).

In the present invention, every time the cumulative print time T reaches the predetermined cumulative print time T1 in the continuous printing, the correction bias ΔV is applied to the magnetic roller 22 in addition to the set value V2 of VmagP (DC) to apply the second patch. It is characterized in that an image is formed and toner density correction between sheets is performed.

That is, every time the cumulative printing time T reaches the predetermined cumulative time T1 in one job, the correction bias ΔV is added to the VmagP (DC) setting value V2 while the VslvP (DC) setting value is maintained at V1. A second patch image is formed, and as described above, the image density detection sensor 43
TD and CTD are calculated on the basis of the detection result of the second patch image by, and Vcon is adjusted (inter-paper toner density correction, second toner density correction).

  FIG. 6 shows an example of a CTD based on the first patch image when correcting the toner density between jobs in the black developing device and a CTD based on the second patch image when correcting the toner density between sheets without applying a correction bias. FIG. 7 is a diagram illustrating an example of the TD of the second patch image when the inter-paper toner density correction is performed in the black developing device.

  In FIG. 6, the horizontal axis represents the integrated print time T, and the vertical axis represents the CTD of the first and second patch images calculated from the detection result of the image density detection sensor 43, and the average value together with the CTD at each time point. Are also shown. In FIG. 7, the horizontal axis represents the time transition from the start of printing as the number of printed sheets, and the vertical axis represents the TD of the second patch image calculated from the detection result of the image density detection sensor 43. In FIG. 7, about 30 printed sheets generally correspond to a printing time of 1 minute, and about 150 printed sheets correspond to a printing time of approximately 5 minutes.

  As shown in FIG. 6, the CTD of the second patch image at the time of correcting the toner density between papers is lower than the CTD of the first patch image at the time of correcting the toner density between jobs executed before and after continuous printing. . For this reason, when Vcon is adjusted based on the CTD of the second patch image, the toner replenishment amount decreases, so the toner amount on the developing roller 23 decreases and the image density of the second patch image decreases.

  Further, as shown in FIG. 7, in continuous printing, for example, a charge of 10V to 20V accumulates on the developing roller 23 with the progress of printing from the start of printing, and the potential of the surface layer of the developing roller 23 increases accordingly. The DS between MSs decreases with the progress of printing. As a result, the amount of toner carried on the developing roller 23 is decreased by the amount corresponding to the decrease in the DS between the MSs, so that a decrease in TD occurs. Accordingly, CTD also decreases.

  In addition, the decrease in TD is greatly reduced by about 1 minute from the start of printing, and then continues to gradually decrease. After about 5 minutes, TD reaches almost saturation. That is, after about 5 minutes, it can be seen that the amount of charge accumulated on the developing roller becomes substantially constant at a predetermined voltage. Here, the DC between MSs decreases about 10 V after about 1 minute from the start of printing and about 20 V after about 5 minutes.

  On the other hand, since Vslv and Vmag applied to the developing roller 23 and the magnetic roller 22 are stopped once printing is completed, the charge on the developing roller 23 is released. For this reason, when correcting the toner density between jobs, no charge is accumulated on the developing roller 23 and the DS between MSs does not decrease, so the TD and CTD of the first patch image do not decrease.

  As described above, even if the TD and CTD are calculated based on the detection result of the second patch image formed in a state where the DS between MSs is lowered in continuous printing, and the toner density correction between sheets is performed, the black developing device 3d It is difficult to appropriately adjust the toner replenishment amount. The color developing devices 3a to 3c also show the same tendency as in FIGS.

Therefore, the inter-sheet toner density correction is performed every predetermined integrated printing time T1, and at this time, the correction bias ΔV is added to the set value V2 of VmagP (DC) to form the second patch image. Further, for example, the correction bias ΔV can be set according to the amount of decrease in DC between MSs so that the DS between MSs approaches the DS between MSs at the start of continuous printing (that is, during correction of toner density between jobs). .

  Further, from the result of FIG. 6 described above, since the decrease in TD reaches approximately saturation in about 5 minutes from the start of printing, the decrease in CTD also reaches approximately saturation. Accordingly, for example, the predetermined integrated printing time T1 is set to 5 minutes, and the inter-paper toner density correction can be performed every 5 minutes.

In the black developing device 3d, the inter-job toner density correction and the inter-paper toner density correction are performed by setting the set value V2 to 120 V, for example, and the correction bias ΔV to the first correction bias ΔV1 (for example, 20 V). FIG. 8 shows an example of the CTD based on the first patch image when correcting the toner density between jobs in the black developing device and the CTD based on the second patch image when correcting the toner density between sheets with a correction bias. FIG.

  As shown in FIG. 8, by setting VmagP (DC) from 120V to 120V + 20V = 140V at the time of paper-to-paper toner density correction, the MS-to-MS DS at the time of paper-to-paper toner correction can be made closer to the time between toner corrections. The decrease in the CTD of the two-patch image can be suppressed, and can be made substantially the same as the CTD of the first patch image. Note that the same results as in FIG. 8 can be obtained in the color developing devices 3a to 3c.

  Next, a first control example of the inter-sheet toner density correction of the developing device of this embodiment will be described. If Vslv and Vmag applied to the developing roller 23 and the magnetic roller 22 are stopped between jobs until the integrated printing time T reaches the predetermined integrated printing time T1, the charge on the developing roller 23 is once lost. Then, electric charges accumulate on the developing roller 23 with the start of continuous printing.

  In view of such a point of view, from FIG. 7 described above, when the inter-sheet toner density correction is performed when the predetermined integrated time T1 is reached in one job, the continuous printing time immediately before the inter-paper toner density correction is performed, that is, the job concerned. The correction bias ΔV is changed depending on whether or not the time from the start of printing until the end of printing immediately before the correction of the toner density between papers (last continuous printing time t) is equal to or longer than a predetermined continuous printing time t1 (for example, 1 minute). You can also.

That is, when the continuous printing time t is 1 minute or more, it is considered that the charge is sufficiently accumulated on the developing roller 23, and the first correction bias ΔV1 (20V) is set to the set value V2 (for example, 120V) of VmagP (DC). ) And V2 + ΔV1 is applied to the magnetic roller 22.
On the other hand, if the immediately preceding continuous printing time t is less than 1 minute, it is considered that the charge accumulated on the developing roller 23 is small, and the second correction that is applied to the set value V2 of VmagP (DC) is smaller than ΔV1. V2 + ΔV2 is applied to the magnetic roller 22 as the bias ΔV2 (for example, 10V).

  FIG. 9 is a flowchart showing a control procedure of this control example. In this flowchart, the inter-paper toner density correction in the black developing device 3d will be described. First, measurement of the integrated printing time T is started (step S1), VslvP (DC) is set to a set value V1, and VmagP (DC) is set to a set value V2 (120 V) (step S2). Next, when the printing quantity and the like are set and printing is started (step S3), it is determined whether or not the accumulated printing time T has reached a predetermined accumulated printing time T1 (here, 5 minutes) (step S4).

If the integrated printing time T has reached 5 minutes, it is determined whether or not the immediately preceding continuous printing time t is equal to or longer than a predetermined continuous printing time t1 (here 1 minute) (step S5). When the continuous printing time t is less than 1 minute, VmagP (DC) is set to the set value V2 (120 V) and the second correction bias ΔV.
A second patch image is formed by setting V2 + ΔV2 (120V + 10V) to which 2 (10V) is added, and toner density correction between sheets is performed (step S6).

On the other hand, when the continuous printing time t is 1 minute or longer, VmagP (DC) is V2 + ΔV1 (120V + 20V) obtained by adding the first correction bias ΔV1 (20V) to the set value V2 (120V).
) To form a second patch image and perform inter-paper toner density correction (step S7). In steps S6 and S7, VslvP (DC) is maintained at the set value V1.

  Then, it is determined whether or not the printing quantity reaches the set quantity in step S3 and the printing is finished (step S8). If the set quantity has not been reached, the process returns to step S4 and the operations of steps S4 to S7 are performed. repeat. On the other hand, if the set quantity is reached in step S8, VmagP (DC) is returned to the set value V2 (step S9), and then the system waits until the next printing operation is started. If the accumulated printing time T has not reached 5 minutes in step S4, the operation similar to the above is performed after step S8.

According to this control example, the DS between MSs can be adjusted in accordance with the state of toner adhesion to the developing roller 23 by varying the correction bias ΔV based on the continuous printing quantity t immediately before the inter-paper toner density correction. Therefore, it is possible to more appropriately prevent the image density of the second patch image from decreasing.

  Next, a second control example of the inter-sheet toner density correction of the developing device according to the present embodiment will be described. FIG. 10 is a diagram illustrating an example of the TD of the second patch image when the inter-paper toner density correction is performed in the low temperature and low humidity environment (10 ° C., 15% RH) in the black developing device. In FIG. 10, as in FIG. 7 described above, about 10 printed sheets correspond to a printing time of approximately 1 minute. The ease of toner adhesion to the surface of the developing roller 23 in the black developing device 3d is affected by environmental conditions such as temperature and humidity, and static electricity is generated particularly under low temperature and low humidity conditions of 10 ° C. and 15% RH or less. Therefore, toner tends to adhere to the surface of the developing roller 23.

  In such a case, as shown in FIG. 10, since the toner adheres to the surface of the developing roller 23 immediately after the start of printing and the charge on the surface of the developing roller 23 accumulates, the DS between the MSs decreases, so that the TD decreases and varies. Increases, and the CTD also decreases accordingly. The color developing devices 3a to 3c also show the same tendency as in FIG.

Therefore, when the temperature / humidity detection result of the temperature / humidity sensor 45 corresponds to a low-temperature and low-humidity environmental condition (here, 10 ° C. and 15% RH or less), regardless of the continuous printing time t immediately before the inter-paper toner density correction, VmagP (DC) is set to the installation value V2 (120V) with the first correction bias ΔV1 (20V).
) To be V2 + ΔV1 (120V + 20V).

As a result, the DC between MSs can be adjusted according to environmental conditions, and image density correction can be performed more appropriately. When the temperature / humidity detection result of the temperature / humidity sensor 45 is greater than 10 ° C. and 15% RH, VmagP ((based on the continuous printing time t immediately before the inter-sheet toner density correction is performed) as in the first control example. DC) is set to the first correction bias ΔV1 or the second correction bias ΔV2.

  FIG. 11 is a flowchart showing a control procedure of this control example. In this flowchart, the inter-paper toner density correction in the black developing device 3d will be described. First, measurement of the integrated printing time T is started (step S1), the set value of VslvP (DC) is set to V1, and the set value of VmagP (DC) is set to V2 (120 V) (step S2). Next, when the printing quantity and the like are set and printing is started (step S3), temperature / humidity detection is performed by the temperature / humidity sensor 45 (step S4), and the integrated printing time T is set to the predetermined integrated printing time T1 (5 minutes). It is determined whether or not it has been reached (step S5).

When the integrated printing time T has reached 5 minutes, it is determined whether or not the environmental condition is a low temperature and low humidity condition (10 ° C. and 15% RH or less) based on the temperature and humidity detection result of the greenhouse degree sensor 45 (step). S6). If it is not a low temperature and low humidity condition, it is determined whether or not the immediately preceding continuous printing time t is equal to or longer than a predetermined continuous printing time t1 (1 minute) (step S7). When the continuous printing time t is less than 1 minute, VmagP (DC) is set to the set value V2 (120 V) and the second correction bias ΔV2 (10 V).
) To which V2 + ΔV2 (120V + 10V) is set, a second patch image is formed, and inter-paper toner density correction is performed (step S8).

On the other hand, when the continuous printing time t is 1 minute or longer, VmagP (DC) is V2 + ΔV1 (120V + 20V) obtained by adding the first correction bias ΔV1 (20V) to the set value V2 (120V).
) To form a second patch image and perform inter-paper toner density correction (step S9). If the low-temperature and low-humidity condition is determined in step S6, the process proceeds to the above-described step S9, and correction of the toner density between sheets is performed by adding a correction bias ΔV1 (20V) to the set value V2. In steps S8 and S9, VslvP (DC) is maintained at the set value V1.

  Then, it is determined whether or not the print quantity reaches the set quantity in step S3 and the printing is finished (step S10). If the print quantity has not reached the set quantity, the process returns to step S4 and the operations in steps S4 to S9 are performed. repeat. On the other hand, if the set quantity has been reached in step S10, the set value of VmagP (DC) is returned to V2 (step S11), and the system waits until the next printing operation is started. If the cumulative printing time T has not reached 5 minutes in step S5, the process proceeds to step S10 and the same operation as described above is performed.

In this control example, since the correction bias ΔV is varied based on the temperature / humidity detection result of the temperature / humidity detection sensor 45, the DC between MSs can be adjusted in accordance with the state of adhesion of the toner to the developing roller 23. A decrease in the image density of the patch image can be prevented. However, if it is possible to detect an environmental condition that affects the adhesion of the toner to the developing roller 23, the temperature and humidity conditions can be set as appropriate. Can also be used.

The inter-paper toner density correction of the present invention is not particularly limited to the black developing device 3d shown in the above control example. For example, the same correction can be performed in the color developing devices 3a to 3c. it can. In the color developing devices 3a to 3c, for example, the set value V2 of VmagP (DC) can be 260V, the correction bias ΔV1 can be 10V, and ΔV2 can be 5V.

  In color printing, transmission of color toner is achieved by setting VslvP (DC) and VmagP (DC) applied to the developing roller 23 and the magnetic roller 22 at the time of forming the first and second patch images to at least twice that of black printing. Can affect the image density detection result of the patch image. Therefore, since the DS between MSs can be adjusted according to the formation state of the first and second patch images, it is possible to more appropriately prevent the image density of the second patch image from decreasing.

  Further, the influence of the charge accumulated on the developing roller 23 during the continuous printing on the DC between the MSs is that the smaller the amount of toner (toner layer) formed on the developing roller 23, that is, the smaller VmagP (DC) is. It becomes relatively large. Therefore, in color printing, the influence of the charge accumulated on the developing roller 23 on the DC between MSs is smaller than that in black printing, and the first and second correction biases ΔV1 and ΔV2 are about ½ of black. Can do.

As described above, by varying the correction bias ΔV according to the set value V2, the DC between MSs can be adjusted according to the influence of the toner adhering to the developing roller 23 on the DC between MSs. It is possible to prevent a decrease in image density. However, the set value V2, the correction bias ΔV, the first correction bias ΔV1, and the second correction bias V2 are not particularly limited to the above, and can be appropriately set according to the decrease in DC between MSs, the device configuration, and the like. .

  The upper and lower limits of the CTD are, for example, 850 and 775 for black printing with a VmagP (DC) setting value V2 of 120 V, and 475 and 425 for color printing with a setting value V2 of 260 V. Can be set. However, the CTD is not particularly limited, and can be appropriately set according to the toner replenishment state, the apparatus configuration, and the like.

  In the present embodiment, at least one of T / C and CTD toner density correction is performed based on the T / C detected by the magnetic permeability sensor 41 and the CTD detected by the image density detection sensor 43. The toner replenishment amount can be adjusted in more detail. However, only CTD toner density correction can be performed.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, the predetermined integrated printing time T1, the predetermined continuous printing time t1, the environmental conditions, and the like shown in the above embodiment are not particularly limited, and can be set as appropriate according to the apparatus configuration. Further, the predetermined integrated printing time T1 and the continuous printing time t1 can be set by the number of printed sheets and the like as long as the printing time can be expressed.

  Further, for example, in the above-described embodiment, a reversal development method in which positively charged toner having a positive charging direction (positive side) is used and the toner is ejected to an exposed portion on the surface of the photoreceptor has been described as an example. The present invention can be applied in exactly the same manner to a developing device using negatively charged toner that is negative (minus side) or a forward developing type developing device that causes toner to fly to an unexposed portion on the surface of the photoreceptor.

  Further, the present invention is not limited to the tandem type color printer shown in FIG. 1, and includes a developing device such as a digital or analog type monochrome copying machine, a monochrome printer, a rotary developing type color printer, a color copying machine, a facsimile, or the like. The present invention can be applied to various image forming apparatuses.

  In the present invention, in the first toner density correction between the printing operations, the control means applies a predetermined reference toner image forming DC bias to the toner supply member, so that the second between the predetermined printings during continuous printing. In this toner density correction, every time a predetermined integrated printing time is reached, a predetermined correction bias is applied to the toner supply member in addition to the reference toner image forming DC bias to form a reference toner image.

  As a result, the second toner density correction can be appropriately performed during continuous printing to prevent the image density from being lowered, thereby preventing image defects. In addition, the control unit varies the correction bias based on the continuous printing time until immediately before the second toner density correction, thereby more appropriately preventing the image density of the reference toner image from being lowered, thereby preventing image defects. Can be prevented.

  In addition, an environmental condition detection unit that detects an environmental condition of the developing device is provided, and the control unit varies the correction bias based on the environmental condition detection result of the environmental condition detection unit. The bias is set to at least twice the DC bias for forming the reference toner image for black image formation, and the correction bias is varied in accordance with the DC voltage for forming the reference toner image, thereby appropriately preventing the image density of the reference toner image from being lowered. Thus, image defects can be prevented.

  In addition, a toner density detecting means for detecting the toner density in the developer is provided, and the control means at least based on the toner density detection result of the toner density detecting means and the image density detection result of the image density detecting means during continuous printing. By executing one of the second and third toner density corrections, the toner density correction can be performed in more detail, and the image density can be more appropriately prevented from decreasing to prevent image defects. Further, by using the image forming apparatus provided with the developing device, it is possible to perform image formation in which a decrease in image density is prevented even during continuous printing.

1a to 1d Photosensitive drum (image carrier)
3a to 3d Developing device 21a First stirring screw 21b Second stirring screw 22 Magnetic roller (toner supply member)
23 Developing roller (toner carrier)
25 Bone cutting blade 30 First bias circuit (voltage application means)
31 Second bias circuit (voltage applying means)
33 Voltage variable device 37 Storage section (storage means)
39 Control unit (control means)
41 Transmission rate sensor (toner density detection means)
43 Image density detection sensor (image density detection means)
45 Temperature and humidity sensor (environmental condition detection means)
100 Image forming apparatus Pa to Pd Image forming unit

Claims (7)

A developer containing at least a carrier and a toner is used,
A toner carrier for supplying toner to the image carrier;
A toner supply member that forms a toner layer on the toner carrier using a magnetic brush;
Voltage applying means capable of applying a DC bias and an AC bias to the toner carrier and the toner supply member;
Image density detecting means for detecting the density of the toner image formed on the image carrier;
A developing device comprising: control means for executing toner density correction in the developer based on an image density detection result of a reference toner image formed on the image carrier by the image density detecting means;
The control means can execute a first toner density correction between printing operations and a second toner density correction between predetermined printings during continuous printing.
In the first toner density correction, a predetermined reference toner image forming DC bias is applied to the toner supply member,
In the second toner density correction, a predetermined correction bias is applied to the toner supply member in addition to the reference toner image forming DC bias every time a predetermined integrated printing time is reached during the continuous printing. A reference toner image is formed.   The developing device according to claim 1, wherein the control unit varies the correction bias based on a continuous printing time until immediately before performing the second toner density correction.   The environmental condition detection means for detecting an environmental condition is provided, and the control means varies the correction bias based on the environmental condition detection result of the environmental condition detection means. Development device.   4. The DC bias for forming a reference toner image for color image formation is at least twice the DC bias for forming a reference toner image for black image formation. Development device.   The developing device according to claim 1, wherein the control unit varies the correction bias according to the reference toner image forming DC voltage. A toner concentration detecting means for detecting a toner concentration in the developer is provided;
The control means can execute a third toner density correction based on the toner density detection result of the toner density detection means, and the toner density detection result of the toner density detection means and the image density during the continuous printing. The developing device according to claim 1, wherein at least one of the second and third toner density corrections is executed based on the image density detection result of the detection unit.   An image forming apparatus comprising the developing device according to claim 1.

Images